I. Field of the Invention
The present invention relates to the field of alkali vapor lamps and, more particularly, toward a power supply control circuit for improving the operation of electrodeless alkali vapor spectral lamps.
II. Description of the Prior Art
Small electrodeless alkali vapor lamps are used as light sources having a particular spectral content for optical pumping and atomic absorption processes. Alkali vapor lamps of this type find widespread application in optically pumped rubidium vapor frequency standards, of both the passive and active type. Such alkali vapor lamps are generally excited by the application of radio frequency energy from an electronic power oscillator.
Proper operation of a frequency standard using an alkali vapor lamp requires an electronic power oscillator or exciter that can reliably start the lamp and maintain constant lamp output under varying environmental conditions. Temperature and/or component variations in the exciter circuit can change the lamp output, both in intensity and spectral distribution. Moreover, some variations in the exciter power supply, such as low frequency ripple, can impress disturbances on the light output. Likewise, variations in the load presented to the exciter by the alkali vapor lamp can induce variations in the excitation power and thereby cause periodic fluctuations in lamp output commonly called "lamp oscillations." This effect is most often seen as audio frequency fluctuations of several percent in light output occurring in the temperature range and excitation level between the all-Rb red mode and the KrRb mixed mode for a rubidium metal vapor lamp containing krypton as a buffer gas. (Other buffer gases such as xenon may also be used.) Such variations can be sufficiently large and slow so as to cause blinking in a lamp which has poor heat dissipation capabilities. Accordingly, lamp oscillations limit the useful operating temperature range of an alkali vapor lamp.
In addition to the above-described variations in lamp output due to temperature changes, component variations, and variations in the exciter power supply, difficulties are often encountered in satisfactorily starting electrodeless alkali vapor spectral lamps using a conventional exciter power supply circuit.
Accordingly, it is an object of the present invention to provide a power supply circuit for an electrodeless alkali vapor spectral lamp which tends to stabilize the lamp output against the effects of temperature and other environmental factors affecting lamp excitation.
Another object of the present invention is to provide a power supply circuit for improving starting characteristics of an electrodeless alkali vapor spectral lamp.
A further object of the present invention is to provide a power supply circuit for reducing the effect of variations in the exciter power supply, such as low frequency ripple, on the light output of an alkali vapor lamp.
A still further object of the present invention is to provide a power supply circuit for reducing lamp oscillations in an energized electrodelss alkali vapor spectral lamp due to variations in the load presented by the lamp to an exciter.
Additional objects and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention can be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.